The present invention relates to a projection zoom lens and a projector for projecting an image onto a screen.
Conventionally, a liquid crystal device is often used as the light valve of a projector. In recent years, in place of a liquid crystal device, devices equipped with a plurality of elements that form images by mechanically changing the directions of reflection of light using a micromachining technique have been realized. One example of such a device is a DMD (digital mirror device or display) in which minute mirror-surface elements (micromirrors) are arranged in an array corresponding to pixels and an image is displayed by controlling the angles of the respective mirror surfaces. Compared to a liquid crystal device, a light modulator (light valve) in which pixels are composed of micromirrors has faster response and produces a brighter image, so that a light modulator is suited to the realization of a compact projector with high luminance and high image quality.
In a DMD, the angle by which the micromirrors rotate when an image is formed is around ±10 to 12 degrees, so that illumination light (source light) is converted into effective or active reflected light that is projection light (modulated light) for forming an image and non-effective or inactive reflection light that is not active in forming the image. Accordingly, to project the active projection light from a DMD using a projection lens, a design is used where the exit pupil is positioned at the final lens located closest to the DMD that serves as the light modulator. In the Japanese Laid-Open Patent Publication No. 2002-148515, an aspherical surface is introduced on the final lens-side of a convex lens positioned just before the final lens of a second lens group for providing a projection zoom lens with a simple and compact construction of around ten lenses.
The effective way to make a projection zoom lens compact is to reduce the number of lenses. However, when the number of lenses falls, the aberration-correcting performance also falls.